.\"
.\" Copyright (c) 2009 Lawrence Stewart <lstewart@FreeBSD.org>
.\" Copyright (c) 2010-2011 The FreeBSD Foundation
.\" All rights reserved.
.\"
.\" Portions of this documentation were written at the Centre for Advanced
.\" Internet Architectures, Swinburne University of Technology, Melbourne,
.\" Australia by David Hayes under sponsorship from the FreeBSD Foundation.
.\"
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.Dd February 4, 2023
.Dt CC_CUBIC 4
.Os
.Sh NAME
.Nm cc_cubic
.Nd CUBIC Congestion Control Algorithm
.Sh DESCRIPTION
The CUBIC congestion control algorithm was designed to provide increased
throughput in fast and long-distance networks.
The CUBIC congestion control algorithm is the default for TCP.
It attempts to maintain fairness when competing with legacy NewReno TCP in lower
speed scenarios where NewReno is able to operate adequately.
.Pp
The congestion window is increased as a function of the time elapsed since the
last congestion event.
During regular operation, the window increase function follows a cubic function,
with the inflection point set to be the congestion window value reached at the
last congestion event.
CUBIC also calculates an estimate of the congestion window that NewReno would
have achieved at a given time after a congestion event.
When updating the congestion window, the algorithm will choose the larger of the
calculated CUBIC and estimated NewReno windows.
.Pp
CUBIC also backs off less on congestion by changing the multiplicative decrease
factor from 1/2 (used by standard NewReno TCP) to 4/5.
.Pp
The implementation was done in a clean-room fashion, and is based on the
Internet Draft and paper referenced in the
.Sx SEE ALSO
section below.
.Sh MIB Variables
There are currently no tunable MIB variables.
.Sh SEE ALSO
.Xr cc_cdg 4 ,
.Xr cc_chd 4 ,
.Xr cc_dctcp 4 ,
.Xr cc_hd 4 ,
.Xr cc_htcp 4 ,
.Xr cc_newreno 4 ,
.Xr cc_vegas 4 ,
.Xr mod_cc 4 ,
.Xr tcp 4 ,
.Xr mod_cc 9
.Rs
.%A "Sangtae Ha"
.%A "Injong Rhee"
.%A "Lisong Xu"
.%T "CUBIC for Fast Long-Distance Networks"
.%U "https://tools.ietf.org/id/draft-rhee-tcpm-cubic-02.txt"
.Re
.Rs
.%A "Sangtae Ha"
.%A "Injong Rhee"
.%A "Lisong Xu"
.%T "CUBIC: a new TCP-friendly high-speed TCP variant"
.%J "SIGOPS Oper. Syst. Rev."
.%V "42"
.%N "5"
.%D "July 2008"
.%P "64-74"
.Re
.Sh ACKNOWLEDGEMENTS
Development and testing of this software were made possible in part by grants
from the FreeBSD Foundation and Cisco University Research Program Fund at
Community Foundation Silicon Valley.
.Sh HISTORY
The
.Nm
congestion control module first appeared in
.Fx 9.0 .
.Pp
This became the default congestion algorithm for FreeBSD in version
.Fx 14.0 ,
replacing
.Xr cc_newreno 4 .
.Pp
The module was first released in 2009 by Lawrence Stewart whilst studying at
Swinburne University of Technology's Centre for Advanced Internet Architectures,
Melbourne, Australia.
More details are available at:
.Pp
http://caia.swin.edu.au/urp/newtcp/
.Sh AUTHORS
.An -nosplit
The
.Nm
congestion control module and this manual page were written by
.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org
and
.An David Hayes Aq Mt david.hayes@ieee.org .
